The UK has signed a £3.4 billion agreement to transfer sovereignty of the Chagos Islands to Mauritius, following the failure of a last-minute legal challenge. Prime Minister Keir Starmer announced the deal on Thursday, describing it as a major step in strengthening the UK’s security relationship with the United States. Under the agreement, Britain relinquishes control of the islands but will lease Diego Garcia—the largest island and home to a key US-UK military base—for 99 years at a cost of £101 million annually. Starmer defended the cost, stating it was necessary for national security and comparable to maintaining an aircraft carrier. The deal, endorsed by allies including the US, Canada, Australia, and New Zealand, comes after a 2021 UN advisory opinion declared that the UK did not have rightful sovereignty over the Chagos archipelago.